1. Field of the Invention
The present invention relates to an audio and/or video signal transmission system suitably used for transmitting the audio signal and the video signal having signals of analog and digital formats in coexistence, and a transmitting apparatus and a receiving apparatus thereof. More in particular, in the case where the audio and video signals of analog and digital formats in coexistence are transmitted from single equipment, the invention is intended for superior display with any of the two types of signals.
2. Description of the Related Art
As an audio or video signal format, a digital format has conventionally been widely used in addition to the analog format. Specifically, such an audio and video signal of digital format are used for recording/reproduction apparatuses such as the video tape recorder and the disk player of digital format or the broadcasting system using the satellite wave or terrestrial wave of digital format.
In the conventional recording/reproduction apparatus and the broadcast receiving apparatus of digital format described above, the reproduction signal and the receive signal of digital format are D/A converted in the equipment and produced as audio and video signals of analog type. The audio and video signals of digital type, however, are more advantageously transmitted in terms of the signal deterioration or the like.
A means for transmitting the audio and video signals of digital format as digital signals uses a format prescribed in IEEE1394, for example. Specifically, in the prescribed format, as shown in FIG. 3, for example, a sync signal (cycle start) is provided for a predetermined period (125 μs). Between these sync signals, an arbitrary number of signal channels (1 to n) called the isochronous packets are inserted.
The isochronous packet has a configuration as shown by A in FIG. 4, for example. Each line of the packet represents one quadlet (four bytes=32 bits), and the first two bytes of the first line of the packet has a value (data length) indicating the length of the following data field. The last two bytes on the first line, on the other hand, has such data as a value (tag) indicating the packet format, a value (channel) indicating the channel number, a value (tcode) indicating the packet identification and a value (sy) used for synchronization.
The first line of this isochronous packet is considered the first head area. Further, the second line has an error correction code (header CRC) for the data in the first header area on the first line described above. Third and subsequent lines of this isochronous packet have the aforementioned data of audio and video signals transmitted over the range indicated by the value (data length) described above. Also, the last line has an error correction code (data CRC) for the data transmitted in the third and subsequent lines.
The audio and video signal data may be transmitted in segments of one, two, four or eight packets as required. In such a case, the temporal data indicating the chronological order for restoring the packets thus segmented are transmitted together with the data of the audio and video signals. Specifically, the first line (third line of the packet) of the data of the audio and video signal transmitted has a second header area, in which the temporal data, etc. are transmitted.
Further, a transmission unit for the control information called the asynchronous packet is arranged between the synch signals described above in the period remaining after transmission of the isochronous packet. The aforementioned sync signals are also transmitted in the configuration of the asynchronous packet. In accordance with the control signal transmitted in this asynchronous packet, the audio and video signals are transmitted between arbitrary units using an arbitrary channel of the isochronous packet.
Specifically, in B of FIG. 4, for example, a configuration of an asynchronous packet is shown for writing control information (data) of one quadlet, for example, in the desired memory or register of an arbitrary apparatus. One line of this packet represents one quadlet, and the first two bytes of the first line contain the recognition code (destination ID) for the destination (write destination) apparatus. The first two bytes on the second line, on the other hand, has a recognition code (source ID) for the source apparatus. These recognition codes (ID) are preset for each apparatus at the time of constructing the system, for example.
The last two bytes of the first line include a label (tl) indicating the series of control status (transaction), a code (rt) indicating the retransmission status, a code (tcode) indicating the type of the packet, and a value (pri) indicating the order of priority. Further, the last two bytes of the second line and the third line include an address (destination offset) such as a memory of the destination and the 4-byte data written on the fourth line. The fifth line, on the other hand, includes the error correction code (header CRC) for each data on the first to fourth lines.
Also, in C of FIG. 4, a configuration of the asynchronous packet for writing control information (data) of at least 1 quadlet into an arbitrary apparatus. The configuration of the first to third lines is the same as that shown in B of FIG. 4. The first two bytes of the fourth line include a value (data length) indicating the length of the following data area, and the last two bytes contain a code (extended tcode) indicating the extended control status (transaction). The fifth line includes an error correction code (header CRC) for each data on the first to fourth lines.
Further, the sixth and subsequent lines include data such as arbitrary control information of at least one quadlet over the range indicated by the aforementioned value (data length). Also, the last line includes the error correction code (data CRC) for the data transmitted on and subsequent to the sixth line. Using these asynchronous packets, the required control information, etc. are written into an address of a predetermined memory or register of the desired apparatus thereby to control the operation or the like of the particular apparatus.
By the way, the asynchronous packet has other predetermined formats of a read request or read response for one quadlet or data of one quadlet, which are not related directly to this application and therefore will not be described. The aforementioned asynchronous packet of the sync signal (cycle start) includes a cycle time code (a value of the timer register of a reference apparatus) in the packet structure of B of FIG. 4, for example.
The provision of this transmission means makes it possible to connect the recording/reproduction apparatus or a broadcast receiving apparatus of digital format described above and an apparatus such as a monitor receiver having an input means of digital format through a bus line. These apparatuses thus can be controlled between each other. By this control operation, arbitrary audio and video signals are transmitted using an arbitrary channel of the isochronous packet between these apparatuses.